Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering SERS is a process in which the Raman scattering cross section of molecules adsorbed onto the surfaces of metals such as silver, copper, and gold is increased by as much as six orders of magnitude. However, the enhancement is short-range and is restricted to the first few layers of molecules adjacent to the surface. As a result, SERS can be used to characterize adsorption of organic compounds onto metals and can be used for non-destructive characterization of interfaces between polymer films and metal substrates as long as the polymer films are not so thick that normal Raman scattering from the bulk of the film is more intense than SERS from the interface. SERS spectra were obtained from bilayers prepared by spin-coating thin films of polymers such as polystyrene onto silver island films and then overcoating them with much thicker films of a second polymer such as polystyrene sulfonate. The spectra were characteristic of the films adjacent to the silver and not the overlayers as long as the thickness of the films adjacent to the substrate was more than about 100 A in thickness. SERS spectra obtained from thick films of an acrylic adhesive spin-coated onto silver were identical to normal Raman spectra of salts of saccharin, a component of the cure system, and to SERS spectra of saccharin, indicating that saccharin segregated to the adhesivesubstrate interface and adsorbed onto the substrate by dissociation. aw